Electrical measuring instrument.



No. 7l'4,|27. Patented Nov. 25, |902.

C. W. ATKINSON. ELECTRICAL MEASUBING INSTRUMENT.

(Application l-ed May 23, 1902.)

2 Sheets-Sheet L (No Model.)

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UNITED STATES PATENT EEICE.

CLAUDE WILLIAM ATKINSON, OF CARDIFF, ENGLAND.

ELECTRICAL MEASURING INSTRUMENT.

SPECIFICATION forming part of Letters Patent No. 714,127, dated November25, 1902.

Application filed May 23, 1902.

.To a/ZZ whom it may concern.:

Be it known that I, CLAUDE WILLIAM Ar- KINSON, asubject of the King ofGreat Britain and Ireland, residing at Cardiff, in the county ofGlamorgan, England, have invented a new and useful Improvement inElectrical Measuring Instruments, (for. which I have made applicationfor Letters Patent in Great Britain under No. 8,503, dated April 1l,1902,) of which the following is a specification.

This invention relates to electrical measuring instrumentsA of a knownprinciple for the measurement of electromotive force, current, andpower, in which a floating body in sensitive and static equilibrium in aliquid is attracted and moved by the electric current to be measured,traversinga coil or coils surrounding or partly surrounding the saidfloating body; and it consists in improvements in the methods ofautomatic compensation for correction of the readings caused byvariation of external temperature.

The use in electrical measuring instruments of a floatingbody carryingan iron or steel wire which is attracted by a solenoid carrying thecurrent to be measured is not novel and has been previously used. Theseinstruments did not, however, prove commercially practicable, owing tothe fact that the density of the fluid in which the floating body wassuspended varied with changes of temperature, and the floating bodybeing made of glass or other material which eX- panded much less thanthe iiuid with rise of temperature the ioat sunk to a lower level as thetemperature rose, and thus the position of the zero ofthe instrument wasvaried and required constant adjustment by hand,l the amount of whichcould not be determined while the instrument was in use. To show theimportance of this source of error, I may give the following gures: Inthe case of a float having a displacement of twenty-five cubiccentimeters and a stem having an area of 0.13 square centimetersfloating in water the oat would sink about half a millimeter for eachdegree centigrade rise of temperature, or with a variation oftemperature of Fahrenheit, such as is met with in most climates, therewould be a variation of nearly seven-tenths of an inch in the positionof the Serial No. 108,674. (No model.)

zero. If, as is already known, instead of using water as the iuid,paraffin-oil be used, then the variation is increased (owing to thegreater expansibility of the oil over water) to nearly four times thisamount, or about two and three-fourths inches, while even if sufficientglycerin be added to the water to prevent its freezing under normalcircumstances the variation of the position ofthe zero would amount tovery nearly an inch for a variation of 60 Fahrenheitin temperature.These variationsin level of the float may be reduced by increasing therelative size of the stem; but in instruments of the type referred tothe magnetic forces obtainable commercially are comparatively small, andtherefore it is not practicable to make the stems large, and in additionunless the stems be kept small the accuracy of the readings is muchimpaired, both owing to the change in the weight of uid displaced by thestern and the increase of other sources of error inherent in thearrangement. Automatic means for guarding against this source of errorwere introduced byL. B. Atkinson and described in the specification ofLetters Patent in the United States of America No. 665,667,dated January8, 1901. Means are there provided for producing a uid having a variationof density with variation of temperature equal to the variation ofdensity of the glass float. This method is a great advance, but has theobject-ion that the adjustment of the density of the fiuid by thedeposition or solution of crystals of the compensating salt is slow, andin such cases as it is necessary to make the float nearly the same sizeas the containing-tube the diffusion of the salt is imperfect if thefloat is at rest, or nearly so. Now my invention consists in means forovercoming these several difficulties, and I provide means for makingthe va- :riations in the density of the oating body equal to thevariations in the density of the fluid. Within the limits of temperatureusually met with the coefficients of cubical eX- pansion of fluids maybe taken to vary from .00025 for 1 centigrade for water to .O01 forpetroleum or .0013 for chloroform, the coecients being rarely constantand these gures being means between about 5 centigrade and 50centigrade. An almost continuous series of uids can be obtainedcommercially between these limits either by taking iuids in a pure stateor by mixing two or more tluids, as water and sulfuric acid in varyingquantities, or by dissolving definite quantities of salts in water. Nowwith the exception 0f ebonite and sulfur, which having mean coeficientsof cubic expansion of .00024 and .0001,7 per 1 centigrade havecoefficients only slightly less than that of water, which I will callClass A, materials may be divided into two other classes- B, thosehaving a coefficient much less than liquids, as glass, (about one-tenthor less that of water,) metals, and woods varying individually, butbeing mostly only relatively little more expansible than glass; 0, thosehaving coeliicients of expansion much greater than liquids, as gases,(almost ifteen times as great as water,) waxes, as stearin, parain-wax,beeswax, (having coefiicients from three to five times as great aswater,) and celluloid.

According to my invention I use a float made of a material that haspractically the same coefficient of expansion as the fluid in which itioats, or I use or combine one or more bodies having a smallercoefficient of expansion than the uid with one or more bodies having agreater expansion, and so produce a float which has a total or meancoefficient of expansion equal to that of the.

fluid. Thus I select air or other suitable permanent gas, and I inclosesuch a volume of this in a float of glass or other material of Class Bby means of an elastic membrane, as india-rubber, that the expansion ofthis volume of airis sufficient to increase the total volume of theiioat by the desired amount, or I take a porous elastic material, likecork, and imprison air in it by means of a waterproof coating of elasticvarnish or paint, and I sometimes make this cork body hollow, so that itonly has thin elastic walls, and by this meansI makea lioat whichexpands the same amount as the fluid it displaees. I may make floatshaving the body divided into two partsone part made of celluloid or ahollow celluloid cylinder and the other part made of wood (whichvexpands much less than water)-the volumes of the two parts being soproportioned that the total variation in volume is equal to that of thefluid displaced. When I use waxes as the compensating material, I formeither an elastic body of cork, which I impregnate with wax, or I form ahollow elastic body of cork, which I impregnate with Wax, or I mold abody, either solid or hollow, out of granulated cork or other suitablematerial and wax, the wax completely filling up the spaces between theportions of granulated material, and thus by proportioning the relativequantities of wax and cork or other material I produce a ioat having acorrect mean coefficient of expansion. To these various types of bodiesI attach stems, which I may make of tube, of glass, metal, celluloid, orother material, for

containing the iron or steel wire, or I form the stern of two pieces ofcelluloid cemented together, so as to inclose the iron or steel wire, orI cement or secure ebonite onto the iron or steel wire, and so make astem having the desired area. When I use stems of ebonite or celluloid,I sometimes shape these so that the area is dierent at different partsof the stem, so as to control the motion under varying forces and causethe scale of the instrument to be more or less open at different partsof the stroke.

In order that the invention may be the better understood, I will nowproceed to describe the construction of the various types of ioathereinbel'ore referred to in relation to the accompanying drawings,reference being had .to the letters marked thereon..

Like letters refer to like parts in the various figures.

Figures 1, 2, 3, and 4 show various constructions of float according tomy invention. Figs. 5 and 6 show enlarged detail views of theconstruction of the stem of the ioat. Fig. 7 showsthe ioat arranged in areceptacle, as an electrometer.

Fig. I represents a oat having a hollow glass bulb a and stem b withamagnetic core or wine c, the lower end of the bulb being closed by anelastic diaphragm d, of indiarubber or the like.

Fig. 2 shows a iioat in which the bulb a is composed of cork walls e andan inclosing coating f, of elastic varnish or paint, so that the gas isimprisoned in the bulb.l If desirable, the body may be made completelyof cork without a hollow space in its interior.

Fig. 3 shows a oat in which the bulb a is composed of an upper chamberg, of celluloid, and a lower portion, of wood, the whole bulb beingcoated with an elastic inclosing coat f, of Varnish or paint.

Fig. a shows a float having its bulb aformed of granulated cork and waxmolded in a suitable mold and having an elastic inclosing coating f.

Fig. 5 shows an enlarged sectional view of the stem of the float made oftwo strips of celluloid g h, cemented together, so as to inclose theiron or steel wire c.

Fig. 6 shows a front View of the same.

This form of construction of stem is very simple and cheap to carry out,and by having the lateral fins or ribs la permits the transverse sectionof the stem to be varied with great facility by cutting away the ribs 7ato a taper'or other form, as shown in Figs. 4- and 6, so that the scaleof the instrument can be opened out or closed up at any part in therange of the index.

If the float of the instrument is made of any material included in ClassA-for example, ebonite-it is made in the usual manner.

The floats shown in Figs. 2 and 4c are provided with aweight Z toproduce stability and IOO IIO

IIS

points m to keep the bulb a out of contact with the sides of the vesselin which they are placed.

Fig. 7 shows a view of one of the floats made according to my inventionadapted to iioat in a liquid O, contained in a receptacle n. Around thereceptacle n is disposed a coil r, through which the current to bemeasured passes, the indication being taken by the position of the floatrelative to a scale p.

Having now described my invention, what I claim, and desire to secure byLetters Patent, is-

l. In an electrical measuring instrument, a float constructed as a wholethat its coefticient of expansion under heat is equalto the coefficientof expansion of the liquid in which the float is supported, incombination with a receptacle for containing the said liquid,substantially as described.

2. In an electrical measuring instrument, a iioat comprising bodieshaving greater and less coefficients of expansion, so that the meancoefficient of expansion of the ioat,as a whole, is equal to the'coeflicent of expansion of the 4:. In an electrical measuringinstrument,

a iloat having a coefficient of expansion under heat equal to thecoefficient of expansion of the liquid in which the float is su pported,having a stern composed of two strips of exible material cementedtogether with a magnetic core between them, substantially as described.

In witness whereot` I have hereunto set my 45 hand in presence of twowitnesses.

CLAUDE WILLIAM ATKINSON. Witnesses:

REGINALD WILLIAM JAMES, CHARLES CARTER.

